This invention relates to semiconductor devices, and, more particularly, to stripe geometry junction lasers.
The stripe geometry semiconductor junction laser was first proposed by R. A. Furnanage and D. K. Wilson (U.S. Pat. No. 3,363,195 issued Jan. 9, 1968) as a means to reduce the number of lasing modes. The stripe geometry also reduces the threshold current for lasing and limits the spatial width of the output beam. Since that early proposal, numerous laser configurations have been devised to implement the stripe geometry concept: (1) the oxide stripe laser, J. C. Dyment et al, Appl. Phys. Let., Vol. 10, pp 84-86 (1967); (2) the proton bombarded stripe laser, L. A. D'Asaro et al, U.S. Pat. No. 3,824,133 issued on July 16, 1974; (3) the mesa stripe laser, T. Tsukada et al, Appl. Phys. Let., Vol. 20, pp. 344-345 (1972) and R. A. Logan et al, U.S. Pat. No. 3,833,435 issued on Sept. 3, 1974; (4) the reversed biased p-n junction isolation laser, H. Yonezu et al, Japan JAP, Vol. 12, pp 1582-1592 (1973); K. Itoh et al, IEEE JQE-11, 421 (1975); G. H. B. Thompson, U.S. Pat. No. 3,780,358 issued on Dec. 18, 1973; R. B. Burnham et al U.S. Pat. No. 3,984,262 issued on Oct. 5, 1976; (5) rib-waveguide lasers, S. E. Miller, U.S. Pat. No. 3,883,821 issued on May 13, 1975; and (6) buried heterostructures of various types, T. Tsukada, J. Appl. Phys., Vol. 45, p. 4899 (1974); T. P. Lee et al, Appl. Phys. Let., Vol. 29, p. 164 (1976) and M. Takusagawa et al, Proc. IEEE Let., Vol. 61, p. 1758 (1963).
The most commonly used configuration for the past seven years, however, has been the proton bombarded, GaAs-AlGaAs double heterostructure (DH) laser. Despite its various shortcomings, lasers of this type have regularly exhibited lifetimes in excess of 10,000 hours and a number have exceeded 100,000 hours (based on accelerated aging tests).
One of the shortcomings of this structure relates to the fabrication of electrical metal contacts to the semiconductor body, in particular the contact to the proton bombarded semiconductor surface. By suitable masking, proton bombardment forms laterally separate, high resistivity zones which bound a narrow (typically 12 .mu.m), low resistivity stripe-like channel under the mask and which extend longitudinally between the laser mirrors. Since forward bias current is constrained by the proton-bombarded zones to flow through the narrow stripe-like channel, and since current densities in these devices are rather high (typically 2000 A/cm.sup.2), a very good metal-semiconductor contact is required at this surface (e.g., a specific contact resistivity of about 10.sup.-5 .OMEGA. cm.sup.2 or less is desirable). The fabrication of a contact of this high quality has been one of the dominant obstacles to the attainment of reproducible, high yield, reliable lasers. Indeed, this problem may become even more severe as narrower (e.g., 8 .mu.m) stripes are contemplated as a means of enhancing control of filamentary lasing. See Dixon et al, APL, 29, 372 (1976).